I haven't seen this posted here, and I did a search with no results, so here goes:
The Method:
1. Gouge.
2. Feint.
Now you have a tagged mob with zero aggro on you. If any other player does something in the mob's aggro radius (heal, buff, etc.), it will switch to them. This is really fun to use in the crowded quest areas of Quel'Danas, as it allows you to tag quest mobs and let other players kill them for you. Then you can go around and loot them when they're done.
This is a great tactic to use on the Fire Elementals at the Throne of Kil'Jaeden. Here, other players don't really care who has the mob tagged since they can get their quest done anyway, and you get to loot all the motes of fire they drop. Great primal farming.
If you want to kill other players, try using it on the Felblood elites in the same area.
I like this better than Vanishing because you keep the tagged mob.